This invent relates principally to an injection-type combustion engine with electric spark ignition which comprises at least one cylinder equipped with an air intake duct, at least one intake valve provided in the cylinder head, at least one fuel injector, and a heating element mounted downstream of this injector and having a heat sink and one or several PTC-pellets mounted on it.
A combustion engine of this type is known from the German Patent Document DE-C-34 26 469 and from the Dutch Patent Document NL-A-8801334.
It was found that of the total exhaust gas emission approximately 50% occurs during the short time period in which the engine has not yet reached its operating temperature. Even exhaust gas catalysts which, under normal conditions, reduce the amount of exhaust gas by approximately 90% do not reach this degree of conversion before the operating temperature of the catalyst has been reached. The conversion starts at a temperature of approximately 300.degree. C. so that, after a cold start, the exhaust gas emission of the engine in a catalyst is not reduced or hardly reduced. Since the temperature level is not high enough for evaporating the fuel (gasoline or alcohol), an additional amount of fuel must be supplied when the engine is cold in order to obtain a combustible mixture. This leads to a high exhaust gas emission. Therefore, when the engine temperatures are low, the fuel consumption and the exhaust gas emission are relatively high. By the preheating of fuel / air mixture, a considerable amount of fuel is therefore also saved because less fuel or no additional fuel is injected. In the case of the initially mentioned combustion engine, the fuel is sprayed onto the heating element which is brought to the desired temperature within a very short time and in the process is also brought to the desired temperature. As a result, the fuel will evaporate better, and a better mixture with the combustion air is also obtained. The heating element is switched off when the engine is warm enough to take over the evaporation of the fuel.
In the case of the engine known from the mentioned German Patent Document DE-C-3426469, the heating element has the form of a pipe which projects into the intake duct of the cylinder and is surrounded by an insulating pipe. The pipe and the insulating pipe are provided with an edge flange, the edge flanges being situated in a recess of the cylinder head and being fixed by the air intake pipe. This construction has the problem that the mounting and exchanging of the heating element is a time-consuming operation. The same problem exists in the case of the engine according to the Dutch Patent Document NL-A-8801334 where the heating element is integrated in a plate which is clamped in between the intake duct and the head of the cylinder.